1. Field of the Invention
The present invention relates to an optical waveguide excellent in all of transparency, a bending property and heat resistance; and a dry film for manufacturing the optical waveguide.
2. Background Art
Optical fibers were mainly used as a transmission medium in fields of a data communication service for family use which is known as FTTH (Fiber To The Home), and long-distance and medium-distance communication for vehicles. Recently, high speed transmission using a light becomes necessary even for a short-distance within 1 m. In this area, optical-waveguide-type optical wiring boards are suitable because they can achieve high density wiring (a narrow pitch, a junction, an intersection, multilayer, etc.), surface mounting, integrating with an electrical substrate, bending at a small radius, what optical fibers cannot achieve.
Optical wiring boards involve generally the following two types. The first type is a substitution for PWB used for printed wiring boards. The second type is a substitution for FPC used for hinges in small terminal device. Since both types require electrical wiring and transmission of low-speed signals for operating VCSELs (Vertical Cavity Surface Emitting Lasers) and PDs (Photo Diodes) which are light receiving elements, IC and the like, an ideal form is a photoelectric composite wiring board on which optical circuits and electric circuits are mounted together.
A polymeric waveguide has been considered to be used for hinge parts of portable terminals because it allows high-speed transmission of a device as well as weight reduction, downsizing and space saving when used in optical circuits. Polymeric materials used for optical circuits are demanded to have transparency within a wave length range used, generally, a visible light range and further demanded to have a bending property when used for hinge parts. For example, in order to downsize a portable terminal, it is required that operation with bending at a small bend radius does not cause a fracture, and a bending property is required severer year after year. In addition, a region where an optical circuit is unnecessary may be formed on a substrate and, then, materials are demanded to have a patterning property.
For parts necessary for optical communication, a mounting step by lead-free solder reflow is required and they have to satisfy reliability tests such as a thermal cycling test, a high-temperature high-humidity test and the like for environmental load. Therefore, polymeric materials are demanded to have heat resistance.
Furthermore, as a process of forming a core layer or a clad layer constituting an optical waveguide, a method of molding a liquid material by a spin coating, bar coating and the like and a method of laminating a dry film material in a solid state at a normal temperature with a press machine on a vacuum laminator are generally used. A dry film material is more desirable because it may become a film by vacuum lamination, resulting in excellent productivity. In this case, such a film is demanded to have tackiness wherein a film appropriately adheres to a substrate and ductility wherein dusts do not generate by breaking an uncured resin layer of a dry film upon handling a film, are required.
As above, with respect to resins used in manufacturing an optical waveguide, before curing, tackiness and ductility are required for an uncured resin layer, and a patterning property is required during processing; and further, for cured products, transparency, a bending property and heat resistance are required.
3. Related Art
Patent document 1 discloses a photosensitive resin composition containing an addition product of carboxyl group-containing resin with an unsaturated compound comprising an α,β-unsaturated double bond and an epoxy group, such as glycidyl acrylate, glycidyl methacrylate and derivative thereof, and methacrylate with an epoxy cyclohexyl group; and a dry film made from the aforementioned composition.
Patent documents 2 to 4 disclose an active energy line-curable optical composition which comprises a compound derived from epoxy resin having a biphenol structure with an epoxy group within a main chain and which provides a cured product excellent in heat resistance, humidity resistance and tenacity, and showing a high refractive index; and a dry film made from the aforementioned composition.
Patent document 5 discloses a photoelectricity mixed substrate having an adhesive layer made of a cured product of a radiation-curable composition comprising a compound having at least one (meth)acryloyl group and at least one epoxy group.
Patent document 6 discloses a heat resistant photosensitive resin composition comprising an unsaturated double bond-containing epoxy resin; and a dry film using it.
In addition, Patent documents 2 and 5 disclose that such a composition may be used for an optical waveguide.
4. Citation List                Patent document 1: JP H08-339081A        Patent document 2: WO 2008/001722A        Patent document 3: JP 2009-046604A        Patent document 4: JP 2009-120737A        Patent document 5: JP 2009-086058A        Patent document 6: JP H07-199457A        